Mains Electricity (OCR GCSE Physics A (Gateway))

Mains Electricity

• Mains electricity is the electricity generated by power stations and transported around the country through the National Grid

• Everyone connects to the mains when plugging in an appliance such as a phone charger or kettle

• Mains electricity is an alternating current (a.c.) supply

• In the UK, the domestic electricity supply has a frequency of 50 Hz and a potential difference of about 230 V

  • A frequency of 50 Hz means the direction of the current changes back and forth 50 times every second

• Mains electricity, being an alternating current, does not have positive and negative sides to the power source

  • The equivalent to positive and negative are called live and neutral and these form either end of the electrical circuit

The live and neutral wires deliver the electricity to the device. The Earth wire is purely for safety

Live, Neutral & Earth Wires

• All electrical appliances are connected to the mains using at least a live wire and a neutral wire

• In the UK, most electrical appliances are connected to the mains using a three-core cable consisting of

  • A live wire

  • A neutral wire

  • An Earth wire

• The insulation covering each wire is colour coded for easy identification:

  • Live wire – brown

  • Neutral wire – blue

  • Earth wire – green and yellow stripes

A diagram showing the three wires going to a mains powered appliance: Live, Neutral and Earth

• The three wires have distinct purposes

The Live Wire

• The live wire:

  Carries the alternating potential difference from the supply to a circuit

• It is the most dangerous of the three wires

• If it touches the appliance without the Earth wire, it can cause electrocution

The Neutral Wire

• The neutral wire:

  Forms the opposite end of the circuit to the live wire to complete the circuit

• Because of its lower voltage, it is much less dangerous than the live wire

The Earth Wire

• The earth wire:

  Acts as a safety wire to stop the appliance from becoming live

• This prevents electric shocks from occurring if the appliance malfunctions or the live wire breaks off and touches the case of the plug

• Every country has a slightly different configuration, with many using two-pin plugs and plug sockets such as in the USA and mainland Europe

  • The earth wire is still present in the two-pin plugs, just more hidden